The invention provides an improved transdermal diffusion matrix for the sustained release of trinitroglycerol. The anti-anginal activity of trinitroglycerol has been well-known for many years. A sustained release of trinitroglycerol through the skin for systemic activity has been known for several decades; see Davis et al, Am. J. Med. Sci., 259-263 (September 1955). Moreover, NITROL (Kremers-Urban) and NITRO-BID (Marion) have been on the market for some time. Gross et al, Archiv fur Toxikologie, Vol. 18, 194-199, 331-334 (1960), noted the sustained release of trinitroglycerol in studies that confirm that trinitroglycerol is delivered through the skin at a steady rate. The rate-determining step for trinitroglycerol systems is controlled by the skin itself. Around 1970, various sustained release forms were proposed as exemplified by Zaffaroni, U.S. Pat. No. 3,942,751, although none of the embodiments disclosed was put into use. Recently, NITRO-DUR (Key Pharmaceuticals, Inc., Miami, Fla.; Keith et al., U.S. Pat. No. 4,291,015) was commercially introduced and favorably received. Two other dissimilar products for the same use have also been proposed for commercial introduction (Searle; Ciba).